Biomedical subjects

Joseph E Maclennan

Publications and source records attributed to Joseph E Maclennan.

4 recordsLinked to original sources

PubMed2007

Electric-field-driven deracemization.

We demonstrate, both theoretically and experimentally, that it is possible to use an electric field to drive the formation of macroscopic chiral (conglomerate) domains from an initially homogeneous fluid racemate. Field-induced segregation is exhibited in a fluid smectic liquid-crystal phase of a racemic mesogen, wherein enantiomerically-enriched domains are readily identifiable by their chiral electro-optical response. The sharp field-generated boundaries that form between opposite-handed domains broaden by diffusion in the absence of field, but reform rapidly if the field is switched on again, providing unambiguous evidence for the field-driven physical separation of enantiomers. A mean-field model successfully describes the steady-state and the dynamic evolution of conglomerate formation.

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PubMed2005

Effect of high spontaneous polarization on defect structures and orientational dynamics of tilted chiral smectic freely suspended films.

The director structure around topological defects and in 2pi walls in the two-dimensional orientation field of thin freely suspended films of tilted chiral smectic liquid crystal is observed to minimize splay of the spontaneous polarization. Concentric ring patterns in the director field unwind more slowly in higher polarization films. These experiments confirm that polarization space charge increases the effective elasticity of static polarization-splay distortions and that it attracts ionic charge, leading to an increase in the effective orientational viscosity of the director field.

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PubMed2004

Field control of the surface electroclinic effect in chiral smectic-A liquid crystals.

The surface electroclinic effect, which causes an azimuthal deviation of the layer normal from the surface rubbing direction in cells of chiral smectic- A liquid crystals, can be eliminated (and even reversed) by applying an electric field during cooling from the isotropic phase. The observed dependence of layer orientation on field strength leads to a model in which the surface electroclinic tilt results from an effective surface electric field. The experiements suggest a general method for controlling the azimuthal layer alignment of chiral smectic cells.

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PubMed2002

Structure and dynamics of ferroelectric liquid crystal cells exhibiting thresholdless switching.

Surface-stabilized ferroelectric liquid crystal cells are usually bistable, with the spontaneous polarization either up or down, perpendicular to the plane of the cell. In materials with high spontaneous polarization the polarization charge self-interaction leads to a monostable structure that exhibits a thresholdless, "V-shaped" switching of the optical response to an applied voltage. With a model that includes the electrostatic self-energy of the spontaneous polarization, we examine the transition from bistablity to monostability as a function of the polar and nonpolar anchoring energies, the liquid crystal elasticity, and the thickness of the alignment layers. Two bistable and one monostable structures are possible. The bistable state is only obtained when the thickness of the insulating alignment layer and the polar anchoring energy are small, or when the spontaneous polarization is small. From linear stability analysis we get analytical expressions for the limits of stability of the structures. Numerical calculations show that in some ranges of the parameters two structures can coexist. We also present the calculation of the polarization fluctuation modes. The lowest one becomes soft at the continuous transitions among the structures and at the limits of stability.

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